book: translation of ch05

Update #12

code/5/5.1.shared.ptr.a.cpp

@@ -0,0 +1,52 @@
+//
+// 5.1.shared.ptr.cpp
+// chapter 05 start pointers and memory management
+// modern c++ tutorial
+//
+// created by changkun at changkun.de
+// https://github.com/changkun/modern-cpp-tutorial
+//
+
+#include <iostream>
+#include <memory>
+
+void foo(std::shared_ptr<int> i)
+{
+    (*i)++;
+}
+
+int main()
+{
+    // auto pointer = new int(10); // illegal, no direct assignment
+    // std::shared_ptr construction
+    auto pointer = std::make_shared<int>(10);
+    auto pointer2 = pointer;    // reference count + 1
+    auto pointer3 = pointer;    // reference count + 1
+    
+    
+    foo(pointer);
+    std::cout << *pointer << std::endl; // 11
+    int *p = pointer.get();             // does not increase reference count
+    
+    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
+    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
+    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
+
+    pointer2.reset();
+    std::cout << "reset pointer2:" << std::endl;
+    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
+    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
+    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
+    
+    pointer3.reset();
+    std::cout << "reset pointer3:" << std::endl;
+    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
+    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
+    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
+    // std::cout << *pointer << std::endl; // reference count equals 0, illegal access
+
+
+    // Before leaving the scope, the pointer is destructed and
+    // the reference count is reduced to 0
+    return 0;
+}